Tracing rejuvenation events in nearby S0 galaxies

Abstract: With the aim of characterizing rejuvenation processes in early-type galaxies, we analyzed five barred S0 galaxies showing prominent outer ring in ultraviolet (UV) imaging. We analyzed GALEX far- (FUV) and near- (NUV) UV and optical data using stellar population models and estimated the age and the stellar mass of the entire galaxies and of the UV-bright ring structures. Outer rings consist of young (<200 Myr old) stellar populations, accounting for up to 70% of the FUV flux but containing only a few % of the total stellar mass. Integrated photometry of the whole galaxies places four of these objects on the green valley, indicating a globally evolving nature. We suggest such galaxy evolution is likely driven by bar induced instabilities, i.e. inner secular evolution, that conveys gas to the nucleus and to the outer rings. At the same time, HI observations of NGC 1533 and NGC 2962 suggest external gas re-fueling can play a role in the rejuvenation processes of such galaxies.